Water Supply Index (WSI) Forecast for January 1, 2016

Snow gauges located behind the Caltrans maintenance station in Alpine County, CA on March 28, 2013.

Snow gauges in Alpine County, photo by DWR

From the Department of Water Resources:

NEW_DWR_LOGO_14inchA Water Year 2016 Water Supply Index (WSI) forecast for conditions as of January 1, 2016 is posted at http://cdec.water.ca.gov/cgi-progs/iodir/WSI.2016 . The accretions forecast will be sent at a later time. The WSI forecast is based on the precipitation and flows through December 2015 and can be summarized as follows:

Sacramento River Unimpaired Runoff Water Year Forecast

(50 percent exceedance)

14.4 MAF

(79 percent of average)

Sacramento Valley Index (SVI)

(50 percent exceedance)



San Joaquin Valley Index (SJI)

(75 percent exceedance)





Unimpaired flows for the 2015-2016 water year have run at the following rates of average:

Region October-December Runoff (%) December Runoff (%)
Sacramento Valley Index (4 rivers) 53 61
San Joaquin Valley Index (6 rivers) 73 88
Tulare Lake Basin (4 rivers) 50 52



Precipitation for the 2015-2016 water year accumulated at the following rates of average:

Region/Index WY accumulated precipitation (%) through December 31, 2015
Sacramento River 97
San Joaquin River 120
Tulare Lake 144
Statewide 101
Northern Sierra 8-Station Index 94 (16.7 inches)
San Joaquin 5-Station Index 121 (15.7 inches)
Tulare Basin 6-Station Index 113 (9.8 inches)



The snowpack as of the morning of January 11, 2016 stands at the following (based on snow sensors):

Region Snow Water Equivalent (inches) % of Average (Apr 1) % of Average (Jan 11)
Northern 13.7 47 104
Central 14.3 48 107
Southern 9.7 38 94
Statewide 12.7 45 103


Weather and Climate Outlooks:  

The 6-day weather forecast for the northern Sierra indicates precipitation on days 2 through 6. Precipitation amounts are expected to be near 5 inches over the period. Freezing levels, currently near 7,000 feet will drop to near 4,500 feet on Thursday and rise up to near 7,000 feet on Saturday.  The forecast for the central and southern Sierra also indicates precipitation on days 2 through 6. The total precipitation for the period is expected to be up to 3 inches for the central Sierra and 1 inch for the southern Sierra.  Freezing levels, currently near 9,000 feet are expected to drop to near 6,500 by Wednesday and rise up to near 8,000 feet by Saturday.

The NWS Climate Prediction Center (CPC) one‐month outlook for January, issued on December 31, indicates increased chances of above normal precipitation for the entire state with the exception of the areas along the California-Oregon border where there are equal chances of above or below normal precipitation. The same outlook predicts above normal temperatures for most of Northern California and along the North and Central coastline. There are equal chances of above or below normal temperatures for the Central and Southern Sierra Nevada as well as most of Southern California.

The CPC three‐month (January‐February-March) outlook, posted December 17, indicates increased chances of above normal precipitation for the entire state with the chances increasing moving south in the state. The same outlook indicates increased chances of above normal temperatures for the entire state.

El Niño conditions are present. Positive equatorial sea surface temperature anomalies continue across most of the Pacific Ocean. El Niño will likely peak during the Northern Hemisphere winter 2015-2016, with a transition to ENSO-neutral anticipated during the late spring or early summer 2016.

Next Update:

The next WSI forecast as well as the first Bulletin 120 forecast for the year for conditions as of February 1, 2016 will be available on February 8, 2016.

Important Links

Full Natural Flow Data:

 Precipitation Data:

Snow Data:

Extended Regional Forecasts:

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